The era of "supertall" structures (buildings over 300 meters) seems to be coming to a close as "megatall" structures begin to take over. These behemoth buildings, which currently include just three skyscrapers—Dubai's Burj Khalifa, the Shanghai Tower and Mecca's Makkah Royal Clock Tower—are categorized as reaching upwards of 600 meters and are expected to more than double by 2020. When it's completed in 2018, The Kingdom Tower in Jeddah, Saudi Arabia will become the first 1km-high building and the tallest in the world. Head to Dezeen to see the rest of the world's upcoming "megatall" structures.